Yttria-stabilized zirconia
Yttria-stabilized zirconia (YSZ) is a zirconium-oxide based ceramic, in which the particular crystal structure of zirconium oxide is made stable at room temperature by an addition of yttrium oxide. These oxides are commonly called "zirconia" (ZrO2) and "yttria" (Y2O3), hence the name. The addition of yttria to pure zirconia replaces some of the Zr4+ ions in the zirconia lattice with Y3+ ions. This produces oxygen vacancies, as three O2- ions replace four O2- ions. It also permits yttrium stabilized zirconia to conduct O2- ions, provided there is sufficient vacancy site mobility, a property that increases with temperature. This ability to conduct O2- ions makes yttria-stabilized zirconia well suited to use in solid oxide fuel cells, although it requires that they operate at high enough temperatures. Applications YSZ has a number of applications: *For its hardness and chemical inertness (e.g., tooth crowns). *As a refractory (e.g., in jet engines). *As a thermal barrier coating in gas turbines *As an electroceramics due to its ion-conducting properties (e.g., to determine oxygen content in exhaust gases, to measure pH in high-temperature water, in fuel cells). *Used in the production of a solid oxide fuel cell (SOFC). YSZ is used as the solid electrolyte, which enables oxygen ion conduction while blocking electronic conduction. In order to achieve sufficient ion conduction, an SOFC with a YSZ electrolyte must be operated at high temperatures (800°C-1000°C). While it is advantageous that YSZ retains mechanical robustness at those temperatures, overall the high temperature necessary is a disadvantage of current SOFCs, and is one of the major barriers to successful commercialization. The high density of YSZ is also necessary in order to physically separate the gaseous fuel from oxygen, or else the electrochemical system would produce no electrical power. *For its hardness and optical properties in monocrystal form (see "cubic zirconia"), it is used as jewelry. *As a material for non-metallic knife blades, produced by Boker and Kyocera companies. *In water-based pastes for do-it-yourself ceramics and cements. These contain microscopic YSZ milled fibers or sub-micrometer particles, often with potassium silicate and zirconium acetate binders (at mildly acidic pH). The cementation occurs on removal of water. The resulting ceramic material is suitable for very high temperature applications. *YSZ doped with rare-earth materials can act as a thermographic phosphor and a luminescent material. *Historically used for glowing rods in Nernst lamps. Related materials include calcia-, magnesia-, ceria- or alumina-stabilized zirconias, or partially-stabilized zirconias (PSZ). Stabilized hafnia is also known. See also *Cubic zirconia *Sintering *Transformation toughening References Further reading * *X. Chen, Z. Mutasim, J. Price, J. P. Feist, A. L. Heyes and S. Seefeldt (2005), 'Industrial sensor TBCs: Studies on temperature detection and durability', International Journal of Applied Ceramic Technology, Vol. 2, No. 5, pp. 414–421. *J. P. Feist, A. L. Heyes and J. R. Nicholls (2001), 'Phosphor thermometry in an electron beam physical vapour deposition produced thermal barrier coating doped with dysprosium', Proceedings of Institution of Mechanical Engineers, Vol. 215 Part G, pp. 333–340. Category:Zirconium compounds Category:Refractory materials Category:Electrochemistry Categoría:Refractario